Renewable energy is energy derived from natural resources that can be replenished, such as sunlight, wind, rain, tides, and geothermal heat. The demand for renewable energy has grown substantially with advances in technology and increases in global population. Although fossil fuels provide for the vast majority of energy consumption today, these fuels are non-renewable. The global dependence on these fossil fuels has not only raised concerns about their depletion but also environmental concerns associated with emissions that result from burning these fuels. As a result of these concerns, countries worldwide have been establishing initiatives to develop both large-scale and small-scale renewable energy resources. One of the promising energy resources today is sunlight. Globally, millions of households currently obtain power from solar energy generation. The rising demand for solar power has been accompanied by a rising demand for devices and materials capable of fulfilling the requirements for these applications.
The performance of glass surfaces of optical components (“optical surfaces”), such as those that transmit, absorb or reflect light when in use, is reduced if/when the optical surface becomes soiled. Soiling generally reduces light transmittance, increases absorbance, and/or increases light-scattering. This is particularly problematic for optical surfaces that are subjected to constant outdoor exposure. Examples of such optical surfaces include, but are not limited to, the glass sun-facing surfaces of photovoltaic (PV) modules, the glass surface of mirrors employed in solar energy generation systems wherein the function of the mirror is to direct incident sunlight to a collecting device or PV module with or without simultaneous concentration of the light, glass lenses (e.g., Fresnel lenses) and glass architectural glazing (e.g., windows). In some applications, glass substrates include a layer of glass and a layer of metal. Mirrors with high specular or total hemispherical reflectance may be used in certain solar energy generation systems, and such mirrors are particularly susceptible to degradation of performance by even small amounts of soiling.
Many solar power systems are installed in dry locations with periods of low relative humidity where dust accumulation is a particular problem. The present inventors have previously developed coating compositions and application methods that provide resistance to dust accumulation (for example, PCT Application No. PCT/US2013/049300, which is incorporated by reference herein in its entirety. However, in other locations where PV arrays or CSP systems are installed and even in some desert locations there are other soiling mechanisms that are due to or are influenced by the presence of water, for example, soiling from soil-water slurries that form during seasonal wet periods, light rain and/or light or heavy condensation. The previously developed coatings provide little resistance to soiling mechanisms that occur due to the presence of water. Other coating compositions have been developed that will readily shed water, but these do not address the problem of dust accumulation and are generally only useful under limited conditions where soiling occurs in the presence of water, for example, they are usually most effective at resisting soiling from soil-water slurries that contain very little soil. There is thus a need for improved coatings that will accomplish both reduction in soiling due to dry dust and a reduction in soiling occurring in the presence of soil and water combinations.